Strand-symmetric models have been used in a maximum likelihood context, although rarely for the purpose of establishing whether strand symmetry is a reasonable assumption. [1]} comment that the reversible models that they fitted to real data seemed to exhibit strand symmetry. [2]} fitted a continuous-time, non-stationary, strand-symmetric model on a known, rooted, four-taxon topology to two genome-scale data sets. They comment that their model is not identifiable on the edges incident to the root, but that it is identifiable on the other two edges. This is not strictly correct. As stated in [3]}, the labelling of states at the internal nodes is not automatically identifiable even for a continuous-time model. Also, as the mapping from the discrete-time process considered in [3]} to the continuous-time process fitted in [2]} is not always unique [6]}, continuous-time models are not identifiable under the results in [3]} without further constraints.
